甘肃一次强对流天气的数值模拟和分析

分析了2005年5月28日甘肃中部强对流天气过程的环流形势,同时利用中尺度数值模式MM5对该强对流天气进行了数值模拟及成因分析。结果表明:这是一次较典型的蒙古低涡型强对流风暴;28日上午在甘肃中南部有不稳定能量区,午后由于局地热对流、地形等抬升作用,不稳定能量发展旺盛,地面冷锋经过甘肃中部时,由于其强烈的抬升作用,低层流场急剧辐合并有强烈的旋转上升运动,触发了不稳定能量的释放,为暴雨、冰雹等强对流天气提供了动力条件。风暴相对螺旋度和能量螺旋度指数高值区对暴雨、冰雹等强对流天气有很好的指示预警作用,强对流天气往往出现在风暴相对螺旋度极大值中心的右侧,出现时间较能量螺旋度最大值出现时间滞后1~2 h。

Numerical Simulation and Analysis of a Severe Convective Weather in Gansu

The general circulation of a severe convective weather occurred in middle part of Gansu province on May 28,2005 are analyzed,meanwhile,this severe convective weather and its cause are simulated and analyzed using the mesoscale model(MM5).The instability energy area has existed in the morning on 28 May and developped very quickly in the afternoon because of the role of terrain and local heat convection.The surface cold front that through the middle part of Gansu causes the low level flow convergent suddenly and revolving,rising intensely.This triggeres the unstable energy release and provides the dynamic condition for the severe convection weather.Analysis of the relative helicity of storm and the energy-helicity index(EHI) show the severe convection weather usually appear at the right of high area of the relative helicity of storm and late 1~2 h of high area of the energy-helicity index.